Nickalls was educated at Eton College where he was known as "Luni" due to his reckless behaviour[1]. He played football with success, and when not engaged in athletically breaking his bones or risking his neck, he would row. At Eton he won the Junior Sculling in 1884, the School Pulling in 1885/86, and School Sculling in 1885. His ability was soon noticed and he secured the four seat in the Eton Eight, carrying off the Ladies' Challenge Plate at Henley Royal Regatta in 1885.

After Oxford, Nickalls joined Leander of which he was Captain in 1892 and 1897 and took the main prizes at Henley Royal Regatta over the next seven years. His Leander crew won the Grand Challenge Cup in 1891 and 1892 and in 1891 he and Ampthill won Silver Goblets again. In 1893 he was in the Magdalen crew that won the Stewards' Challenge Cup and he also won the Diamonds again against Kennedy. In 1894 he won Silver Goblets partnering his brother Vivian, whom he defeated in the same year in the Diamonds. Vivian Nickalls became a member of London Rowing Club and Guy joined them to win the Stewards in 1895 and the brothers also won Silver Goblets again that year. However Guy lost Diamonds that year to Rupert Guinness. In 1896 Nickalls had three wins – the Grand with Leander, Stewards with London Rowing Club and Silver Goblets with his brother. In 1897 he won Stewards with Leander and Silver Goblets with E. R. Balfour.[6]

After a break of several years, Nickalls was a member of the Leander crew that won the Grand in 1905, but over the next few years the dominant eight in the event was the Belgian crew from Royal Club Nautique de Gand. Nickalls was a member of the winning crews in the Stewards in 1905, 1906 and 1907. In 1908 he was a member of the Leander eight, which was assembled to challenge the Belgians rowing at the 1908 Summer Olympics, and beat them to win the gold medal for Great Britain.[7]

From 1913 to 1916 Nickalls coached Yale, enticed to New Haven by Averell Harriman and a sufficient salary to help see his two sons through Eton. Though his Yale crews won two of the three years he was there, Nickalls found the environment stressful and foreign. He was partly to blame, by spouting opinions better left unsaid or, if said, certainly not within earshot of the attentive rowing press. Yet such remarks – "Their paddling is bad, their rowing, worse" (about the Yale 1916 crew){[8]—were wholly in line with his personality: as O.U.B.C. President, he nearly scotched the 1890 Boat Race by calling the Cambridge crew “probably a poorer lot than usual” in an official letter to his counterpart, S.D. Muttlebury.[9]

Nickalls tried to join the army in 1914 on the outbreak of war, but was turned down on account of age. By late 1917 the army had a change of heart, sending him to France, then age fifty, as a Captain in the 23rd Lancashire Fusiliers in charge of physical and bayonet training. After the war, he resumed his career as a stockbroker.

When Zürich Rowing Club won the Stewards on 6 July 1935, Nickalls told Gully "Thank God I have been spared to see what I believe to be the finest four of all time". The next morning, he was in car crash near Leeds en route to Scotland for a fishing holiday, and died in hospital the following evening. On the same day his school friend and rowing partner, Lord Ampthill, died.

Nickalls married Ellen Gilbey Gold in London in 1898. She was the sister of Sir Harcourt Gold, who was chairman of Henley Royal Regatta from 1945 to 1952 and Chairman of the ARA from 1948 to 1952. Their son Guy Oliver Nickalls was also a rower who competed in two Olympic games. Nickalls snr. co-authored a history of the noted Irish actor and comedian Thomas Doggett and his eponymous rowing race.[10]

^"Tom Nickalls Dies in England". New York Times. 12 May 1899. Retrieved 24 March 2011. Tom Nickalls, father of the famous scullers, Guy and Vivian Nickalls, died to-day at Pattison Court, at the age of seventy-two. When a boy Mr. Nickalls ...

^"Tom Nickalls Dead". Daily Mail and Empire. 12 May 1899. Retrieved 24 March 2011. Nickalls, father of the famous scullers, Guy and Vivian Nickalls, died to-day at court, Redhill, at the age of 72 years. When a boy, Mr. Nickalls ...